1. Field of the Invention
The present invention relates to a mobile terminal, and more particularly, to a power control apparatus for a mobile terminal.
2. Background of the Related Art
FIG. 1 is a schematic block diagram showing the power control mechanism of a conventional mobile terminal. As shown in FIG. 1, the transmission power source control includes an intermediate frequency automatic gain controller (IF AGC) 1 for performing intermediate frequency (IF) gain control based on a transmission intermediate frequency signal TX_IF). An up-mixer 2 for up-converting the IF signal by mixing the adjusted IF signal with a local oscillation frequency generated from a local oscillator 6. A driver amplifier 3 for amplifying the up-converted frequency signal, and an image filter 4 for removing harmonics of the up-converted frequency signal. A power amplifier module (PAM) 5 for amplifying the band-passed frequency signal, and power control means 7 for adjusting an closed-loop gain of the power amplifier module 5. An IF gain control means 8 for outputting an IF gain control signal to control the gain of the IF gain controller 1.
In the transmission power control described above, the transmission power of a mobile terminal is controlled by adjusting the gain of the IF automatic gain controller 1 under the control of a mobile station modem (MSM). That is, the MSM sends a transmission gain control signal (TX_AGC_ADJ) to the IF gain control means 8 to transmit a transmission power in corresponding to a reception power, and the IF gain control means 8 generates a power suitable for the transmission power based on the transmission gain control signal (TX_AGC_ADJ) and sends the same power to the IF automatic gain controller 1.
Further, in order to restrain the generation of the harmonics and transmission noises of the transmission power of a mobile terminal and minimize the power consumption, a level of a reference voltage (PAM Vref) of the power amplifier module (PAM) that consumes the most current should be appropriately controlled. The reference voltage (PAM Vref) of the PAM 5 is obtained by the following equation:
                    Vref        =                              VCC_TX            ×            R2                                R1            +            R2                                              (        1        )                            wherein the resistors (R1, R2) distribute a voltage level of the transmission power source (VCC_TX) to be applied as the reference voltage (PAM Vref) to the PAM 5 according to a power mode within the power control means 7, and are connected in parallel with each other when a switch SW1 is turned off.        
In the power control means 7, the switch SW1 is turned on or off depending on a power mode select signal (PA_R1) from the MSM. In a low power mode (PA_R1=LOW), the switch SW1 is turned off to decrease the gain of the power control means 7, and further restrain the occurrences of harmonics, therefore, reduce the power consumption. Meanwhile, in a high power mode (PA_R1=HIGH), the switch SW1 is turned on, and the transmission voltage (VCC_TX) is provided to the PAM 5 as a reference voltage for obtaining a sufficient gain.
In equation (1), if the switch SW1 of the power control means 7 is turned to enter the high power mode, R1 becomes 0 and Vref becomes equal to VCC_TX. When the power mode is converted from the lower power mode to the high power mode, the gain of the PAM 5 abruptly jumps up. A switch SW2 of the IF gain control means 8 is then turned on for decreasing the gain of the IF automatic gain controller 1, and therefore minimize the influence from the abrupt gain change.
After the power mode is converted, the MSM gradually increases the level of the transmission gain control signal (TX_AGC_ADJ) so as to increase the gain of the IF automatic gain controller 1. However, the conventional transmission power control mechanism has a drawback that the transmission power jumps up (see FIG. 2), hence, first noise unavoidably occurs. When the gain control start point of the IF automatic gain controller 1, which decreases the gain of the IF automatic gain controller 1, and the gain control start point of the PAM 5, which increases the gain of the PAM 5, are not identical with each other while adjusting the abrupt change of the transmission power during mode conversion from the low power mode to the high power mode, the jumps up occurs.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.